1. Field of the Invention
The present invention relates to a writing method and a disk recording apparatus, and relates in particular to a writing method employed when a rewritable disk recording medium is used for a computer and to a disk recording apparatus that uses the writing method.
2. Description of the Related Art
A DVD-RAM, a DVD-RW, a DVD+RW and a CD-RW are well known rewritable optical disk recording media. But for one of these media to be employed in a computer as though it were a hard disk drive, the reproduction reliability of recorded information must be fully ensured.
A process for linking recording tracks on which information is recorded is employed for the additional writing or rewriting of information. When, for example, a CD-RW is used, to prevent data destruction during the writing or rewriting of additional data, dummy data corresponding in size to a sector is added before and after the linked tracks. That is, redundant data are added before and after the linked tracks to prevent data destruction when the overwriting of data is performed. On the contrary, for a DVD-RW and a DVD+RW, a zero link method is employed whereby the amount of redundant data required for linking is reduced as much as possible, and a reduction in the memory capacity of a disk is avoided (see JP-A-2000-311449, pp. 9 to 10 and FIGS. 4 and 5).
As for the designation of a linking location, phase modulation is performed for wobbled grooves pre-engraved on the track side face of a disk, or sync signal and address information recorded as a land prepit is reproduced, so that even on an unrecorded disk the recording location can be specified.
As is described above, since the dummy data for each sector is added during the additional writing or rewriting performed for the CD-RW, data will not be destroyed even when a slight recording shift occurs. However, since the zero link method is employed for the additional writing performed for the DVD-RW and the DVD+RW, data destruction will occur if there is a slight recording shift. The problems presented by the zero link method will be specifically described while referring to FIGS. 2A, 2B and 2C.
FIG. 2A is a diagram showing the ideal zero linking state. Dummy 8T (T denotes a channel bit that is the basic unit of a recording mark length on a disk) data are added before an ECC block (an error process unit) to be recorded, and the recording of dummy data is begun at the linking location (16th wobble location) at the 8T terminal end of the ECC block, and is halted at the linking location (16th wobble location) at a distance 8T from the terminal end of the ECC block to be recorded. In this manner, the rewriting or additional writing is performed for each ECC block.
The linking location is designated by specifying the wobble location and the head of the ECC block. The head of the ECC block is designated by an ADIP address and a data ID, and the linking location is specified by designating the wobble location through the detection of an ADIP sync phase modulator. The linking location can also be designated by a data ID or the detection of the timing for a frame sync. In the ideal zero linking state, the disabling of the reproduction of an ECC block, caused by a burst error inside an ECC block, does not occur.
FIGS. 2B and 2C are diagrams showing a problem encountered when a frame recorded on a specific track is advanced a distance yT (y is a positive number) from the wobble location on the disk in order to record, on a specific track, data (RMW: read modify write) for a specific ECC block. In the following explanation, the frames are recorded while the wobble position and the frames are shifted a −1 wobble (−32T) distance.
As a factor that depends on the disk recording apparatus, the shifting of a frame relative to the wobble location is affected by a jitter included in a 1T recording clock that is generated in synchronization with the reproduction wobble. For fast recording especially, a cyclic error due to the jitter is accumulated as the frequency of the recording clock is increased.
Further, another factor that depends on the disk recording medium can be the deterioration of the quality of a reproduction wobble signal due to a wobble formation failure, and scratches or dust on the disk.
FIG. 2B is a diagram for explaining a problem that occurs at the RMW front end. When, while using a specified wobble location as a reference, the rewriting of an ECC block is performed for a recording track wherein the frame is shifted a distance yT from the wobble location, the frame sync at the ECC block boundary, which exists as a mark on the track before rewriting is performed, remains, not overwritten.
An explanation will now be given for the detection window operation performed for a frame sync required for the reproduction of a recording track wherein rewriting is performed, and the occurrence of a demodulation error. For a recording track located before a rewriting interval, the frame sync detection is stably performed, and the demodulation unit is designated for the frame data in synchronization with the frame sync detection. Therefore, information recorded before modulation is reproduced.
However, near the boundary of the ECC block for which the rewriting is performed, a detection window is opened by predicting the next frame sync location based on the current frame sync detection location. Therefore, the demodulation of frame data is not performed in synchronization with the frame sync positioned at the head of the rewritten ECC block. That is, since the detection of a frame sync signal is skipped, correct information cannot be obtained following the linking location at the rewritten ECC block boundary, and this phenomenon is transmitted as a burst error inside the ECC block.
Even when a frame sync is undetected, the frame sync detection window is cyclically protected during a period equivalent to the length of several frames. When the times at which the frame sync is undetected are equal to or greater than n (n is a natural number), i.e., when a lock out of the frame sync is detected, the operation is shifted to the pulling-in of a frame sync, and the cyclic protection is resumed beginning with the detection of a first frame sync. The frame data included in an interval beginning at the head of the rewritten ECC block and continuing to the pulling-in of the frame sync is a burst error inside the ECC block, and the reproduction of the ECC block that has been rewritten may be disabled.
FIG. 2C is a diagram for explaining a problem occurring at the RMW rear end. A problem occurs in FIG. 2C that is similar to the one in FIG. 2B, and the frame sync at the ECC block boundary, which was present before the data rewriting, may be lost through overwriting. In this case also, in the ECC block following the linking location, a burst error is transmitted until the pulling-in of the frame sync detection window is performed.
While referring to FIGS. 2A to 2C, the frame has been advanced from the wobble location a distance yT. However, the same problem occurs when the rewriting for each ECC block is performed for a recording track wherein, from the wobble location, the frame is shifted to the rear the distance yT.
Further, since the DVD and the CD are removable recording media, the reproduction compatibility between the disk drives should be maintained, and the occurrence must be prevented from a phenomenon wherein a drive cannot reproduce data recorded on a disk for which rewriting is performed while frames are being shifted.